[Transforms] Add cos(fabs(x)) -> cos(x) to SimplifyLibCalls

We have this for InstCombine, but forgot to add it for SimplifyLibCalls.

Author: AZero13

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -2491,8 +2491,8 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     Value *X;
     Value *Src = II->getArgOperand(0);
     if (match(Src, m_FNeg(m_Value(X))) || match(Src, m_FAbs(m_Value(X)))) {
-      // cos(-x) -> cos(x)
-      // cos(fabs(x)) -> cos(x)
+      // cos(-x) --> cos(x)
+      // cos(fabs(x)) --> cos(x)
       return replaceOperand(*II, 0, X);
     }
     break;

llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp

@@ -1934,8 +1934,10 @@ static Value *optimizeTrigReflections(CallInst *Call, LibFunc Func,
   case LibFunc_cos:
   case LibFunc_cosf:
   case LibFunc_cosl:
-    // cos(-X) --> cos(X)
-    if (match(Call->getArgOperand(0), m_FNeg(m_Value(X))))
+    // cos(-x) --> cos(x)
+    // cos(fabs(x)) --> cos(x)
+    if (match(Call->getArgOperand(0), m_FNeg(m_Value(X))) ||
+        match(Call->getArgOperand(0), m_FAbs(m_Value(X))))
       return copyFlags(*Call,
                        B.CreateCall(Call->getCalledFunction(), X, "cos"));
     break;